Nuts or fasteners or other objects having internal threads are commonly produced through the use of a rotating tap which cuts a spiral thread pattern into a wall of an axial bore in the object to be tapped. In conventional or prior machines designed to mass produce nuts or other types of threaded fasteners, the tap typically is attached to one end of a shank. (The terms nuts, fasteners, blanks, workpiece, etc. may be used substantially equivalently herein and are considered equivalents with respect to tapping thereof according to the disclosed and claimed invention.) The opposite end of the shank is bent or offset from the length of the shank to provide a torque arm for engagement with a tap driver to rotate the shank and the tap. The shank and tap are rotated at a constant speed by a tap driver. The axial bore of a nut or fastener blank is aligned with the linear axis of the tap and shank and the nut or fastener blank is pushed onto and over the tap by a pusher or other advancement mechanism. The rotating tap cuts a spiral thread pattern into the advancing nut blank bore. Such machines are in essence two machines, the tap driver for providing a rotating tap and the nut or fastener blank pusher, both working in conjunction to produce an object with internal threads.
Such machines often are referred to as nut tapping machines, fastener tapping machines or by similar names.
After the axial bore of the fastener blank is tapped by the cutting threads of the tap, the newly tapped fastener remains on the shank. The tapped fastener is then pushed along the length of the shank away from the tap by the progression of successive nuts which are similarly tapped and pushed along the rotating tap and are held within a cylindrical sleeve positioned about the straight portion of the shank. As the tapped nuts or tapped fasteners (also referred to herein as threaded nuts or fasteners) ultimately arrive at the bent end of the shank, fasteners drop off the bent end into a receptacle or other type of receiving system.
U.S. Pat. No. 3,510,896 discloses such an exemplary conventional tapping machine having a bent shank supporting a tap used for cutting threads into nuts. The tapped nuts fall off the bent end of the shank into a collecting housing as is described herein. U.S. Pat. No. 4,229,126 discloses another conventional machine for tapping nuts with a pusher which pushes the nut blanks onto the tap and along the shank.
There are many problems associated with the existing machines and methods employed in the above described tapping operation. One principal problem involves the fastener pusher for holding and advancing the fastener blanks also referred to as workpieces as they are brought into contact with and along the rotating tap. In a typical tapping machine employing a pusher, the bore of a single fastener blank is positioned or otherwise aligned with the rotational axis of the rotating tap and shank. The pusher pushes the blank onto and along the rotating tap and continues to push the blank until it has completely passed over the cutting teeth of the tap. The pusher thereafter must retract fully away from the tap to allow a subsequent fastener blank to be put into position and/or to be aligned in front of the tap for subsequent tapping. During the time necessary to allow the pusher fully to retract, the tap and shank continue to rotate despite the fact that no tapping is taking place.
Thus, such an existing machine is engaged in an actual tapping process only a fraction of the time it is operating and, in fact, is operating at a much lower efficiency than it would otherwise operate if fasteners were being tapped substantially continuously without having to wait for the pusher to retract after each piece is tapped. The productivity of such machines is seriously limited due to such inefficiency. To compensate for this limitation, such machines frequently are run at speeds in excess of the designed parameters thereof, often more than twice as fast as the designed maximum speed. This results in excessive and premature wear of all of the components of the machine, especially the tap. Such component(s) therefore have to be replaced more frequently, and during such servicing of the machine further production time is lost. The cost of replacement parts and of lost productivity time increases the cost of operating the machine and, or course, the cost of the parts produced.
The present invention provides a method and apparatus for continuously advancing a series of nut or fastener blanks (or other equivalent or similar workpieces) onto a rotating tap so that the tap is continuously or substantially continuously engaged in a tapping process throughout the period of operation of the machine.
Another problem with existing fastener tapping machines involves the apparatus by which fastener blanks are securely and accurately held in position as they come into contact with the rotating tap. This has heretofore been accomplished through the use of individual block guides which, if correctly aligned, guide the blank onto the tap and prevent the blank from rotating as it is being tapped. Typically, the individual block guides would have to be adjusted manually so as to be aligned properly with the tap. This often involves relying on the visual alignment of the block guides and tap. Accordingly, the adjustment of such guides requires a great deal of time and labor, further reducing the productivity of such machines. As a result, substantial set-up time is required to provide proper alignment. Moreover, each time the machine tooling is changed, for example, to change taps or to accommodate different size nuts or other types of fasteners, the alignment procedure must be repeated, resulting in additional production losses.
The present invention overcomes such shortcomings found in existing machines by providing a modular fastener blank holding and guidance apparatus which is combined with a continuous nut blank advancement means. The combination of the fastener blank advancement apparatus with the holding and guidance means in the form of a modular unit simplifies the adjustment, alignment construction, operation, maintenance and retooling of the machine as described below.
Another problem associated with existing fastener tapping machines involves the difficulty of changing, when desired, the machine tooling such as the tap and the shank. In the operation and maintenance of such machines, it is necessary on a regular basis, for example, at the end of a production run, to remove from the machine the shank which supports the tap. The shank is removed to permit the tap to be changed and to remove the nuts which remain along the length of the shank at the end of a production run. In the past, to remove the shank it has first been necessary to disengage the bent end of the shank from the tap driver used to rotate the shank. This typically requires that the tap driver, usually a large and massive assembly, first be moved relative to the shank, rather than the shank being removed from the tap driver. After the tap driver is moved enough to provide adequate clearance the shank is then pulled along its longitudinal axis from a bearing housing which supports the shank. Removal of the shank in this manner is extremely difficult and time consuming, particularly after a long production run resulting in heat induced expansion and binding of the close tolerance parts. Also, the tapped fasteners which remain about the length of the shank at the end of a production run tend to complicate removal of the shank. The entire procedure requires a great deal of time and labor, further reducing the efficiency and productivity of the machine. Furthermore, a relatively large space is required surrounding the machine to provide space for the displaced tap driver and to provide clearance to withdraw the shank axially from its bearing housing.
The present invention, provides for convenient removal of the shank without having to displace the tap driver away from the shank. Moreover, the present invention further provides an improved shank mounting and bearing structure that provides secure support for the shank. The mounting and bearing structure permits unobstructed rotation of the shank and provides protected guidance for the fasteners as they move along the length of the shank.
Still another problem associated with existing fastener tapping machines involves the manner in which the rate of rotation of the tap is synchronized with the rate of advancement of the fastener blanks. In order to achieve tapped threads of the correct pitch, the rate of rotation of the tap must be synchronized with the rate at which the fastener blanks are advanced as will be appreciated. Typically, in existing machines, such synchronization is accomplished by the individual adjustment of the tap driver speed relative to the advancement rate of the fastener blank pusher. This adjustment typically requires physically changing cams and/or gears which actually drive the tap driver and pusher. Such method of synchronization is often by trail and error and is burdensome, time consuming and difficult.
The present invention provides an improvement for obtaining such synchronization by way of an electrical control circuit which electrically links the tap driver with the fastener blank advancement mechanism so that the two remain in proper synchronization.
Another problem associated with the existing nut and fastener tapping machines occurs in the slot of the tap driver which receives and engages the bent end of the shank to effect to power rotation of the shank and tap. As tapped fasteners reach the bent end of the shank inside the tap driver and are forced off the bent end of the shank, the fasteners come in direct contact with the interior walls of the slot in the tap driver head. This repeated and continuous contact of the fasteners with the tap driver slot rotating at high velocity rather quickly results in excessive wear and deterioration and deformation of the shape of the slot of the tap driver. The flat walls which define the slot in the tap driver are quickly abraded to the point where the formation of the slot is substantially deformed. A tap driver with a deformed slot does not provide accurate engagement and rotation of the tap to continuously produce tap fasteners of consistent acceptable quality.
The present invention provides an improvement for overcoming rapid and excessive abrasion and deformation of the slot in the tap driver by providing a roller mechanism at the top edge of the exiting side wall of the slot. Tapped fasteners which reach the bent end of the shank touch only the roller mechanism incorporated into the interior of the slop in the tap driver to eliminate friction and abrasion of the tap driver by the fasteners.
As will be appreciated, the present invention overcomes the aforementioned shortcomings of known fastener tapping machines and provides an apparatus and method for continuous and uninterrupted tapping of blank fasteners as are summarized and described in detail below.